The intervertebral discs of the human spine are prone to degeneration. In particular, the intervertebral discs located in highly mobile regions of the spine are disproportionately prone to degeneration, primarily due to overt and covert trauma to the tissue that occurs in the course of repetitive activities. Such trauma tends to disrupt the internal architecture of the disc and leads to bulging, herniation or protrusion of pieces of the disc, and the eventual collapse of the disc space. The resultant mechanical and/or chemical irritation of the surrounding neural elements, such as the spinal cord and nerves, may cause pain, inflammation and varying degrees of osteoarthritis and disability. Additionally, the loss of disc space height relaxes tension on the longitudinal spinal ligaments, thereby contributing to varying degrees of spinal instability.
Various treatments have been developed to treat such intervertebral disc degeneration. Many of these treatments involve the fusion of adjacent vertebra in order to limit their ability to move independently from each other, as such independent movement tends to exacerbate the degeneration of the interposed disc. These prior spinal fusion operations often involve either the passive grafting of bone between the surfaces of proximate articular processes in a facet joint that is denuded of synovium, or they involve the mechanical fixation of the facet joint with a simple screw.
These prior treatments, while fairly adequate for their purpose, suffer from a number of drawbacks. For example, operations that involve the passive grafting of bone require additional instrumented fixation of the spine to prevent dislodgement of the bone grafts from between the articular surfaces of the joint. Operations involving the mechanical fixation with a simple screw are largely adjunctive, that is, the screw alone is not sufficient as a means for fixing the facet joint. The long term success of this procedure is usually dependent upon bony union occurring elsewhere between the adjacent vertebral elements being fused, i.e., interbody or inter-transverse postero-lateral fusions.
Thus, there is a longfelt need for a facet fixation device that can be utilized either directly in a stand alone facet fusion procedure or as an adjunctive fixator to be utilized when other forms of spinal fusion are employed, e.g., as back up for an anterior fusion. There is also a longfelt need for such a device that may be deployed radiographically or through endoscopically-assisted minimally invasive approaches.